Most people who have polymyositis get diagnosed between the ages of 30 and 60. It’s very rare in children, and it affects women more often than men.

Symptoms

The symptoms of polymyositis are caused by inflammation in the muscles. The muscle weakness affects both sides of the body equally.

The condition tends to target the muscle groups that are closest to the trunk of the body -- the hips, shoulders, thighs, upper arms, upper back, and neck.

If you have it, you may notice you have trouble lifting your arms over your head, walking up flights of stairs, rising from a chair, or carrying things. In some cases, it may be hard to swallow food, but this is unusual.

You may or may not have pain in the areas where the muscles are weak. Over time, the muscles may atrophy, meaning they waste away or become less bulky. The condition often worsens slowly, and you might not notice symptoms for months.

Muscle weakness may be one of the first symptoms you do notice. You may also feel you just can’t do all the things you used to. You may also have:

Raynaud’s phenomenon, a condition in which the fingers or toes become very cold and discolored due to blood-flow problems.

Diagnosis

There are no simple tests to diagnose polymyositis. It often takes time before doctors know for sure you have it.

Your doctor will consider your medical history, and your family’s, to rule out other conditions. You may also get tests such as:

EMG (electromyography), which checks to see if the patterns of electrical impulses in the muscles are normal or not)

Muscle biopsy, which can show whether or not the muscle tissue is inflamed. Your doctor will take a small sample of your muscle for testing. You may need to get an MRI to help your doctor find a good spot to biopsy.